Growth—Development—Structure and Function—Waste and Repair—Adaptation—Cell-Life—Genesis—Nutrition and Reproduction—The Germ-Cells
Growth.—Perhaps the widest and most familiar induction of Biology, is that organisms grow. But there is growth in crystals, in terrestrial deposits, in celestial bodies; in fact, growth, as being an integration of matter, is the primary trait of evolution; it is universal, in the sense that all aggregates display it in some way at some period. "The essential community of nature between organic growth and inorganic growth is, however, most clearly seen on observing that they both result in the same way. The segregation of different kinds of detritus from each other, as well as from the water carrying them, and their aggregation into distinct strata, is but an instance of a universal tendency towards the union of like units and the parting of unlike units (First Principles, § 163). The deposit of a crystal from a solution is a differentiation of the previously mixed molecules; and an integration of one class of molecules into a solid body, and the other class into a liquid solvent. Is not the growth of an organism an essentially similar process? Around a plant there exist certain elements like the elements which form its substance; and its increase in size is effected by continually integrating these surrounding like elements with itself." And so on.
Passing over the far-fetched statement that the deposit of sediment in distinct strata illustrates the universal tendency towards the union of like units and the parting of unlike units, we must point out that Spencer begins his discussion of organic growth by describing it in such general terms that its essential characteristic is lost sight of. A minute crystal of alum is dropped into a saturated solution of alum, and it grows rapidly under our eyes out of material the same as its own, but the living creature grows larger at the expense of material different from its own. The grass grows at the expense of air, water, and salts, and the lamb grows at the expense of the grass. Though the living creature cannot, of course, transform one element into another, and must have carbon, hydrogen, oxygen, nitrogen, etc., in its food, it utilises materials chemically very different from its own complex compounds.
Spencer's inductions as to growth were the following:—
(1) The growth of an organism is dependent on the available supply of such environing materials as are of like natures with the matters composing the organism.
(2) Other things being equal, the degree of growth varies according to the surplus of nutrition over expenditure.
(3) In the same organism the surplus of nutrition over expenditure differs at different stages, and growth is unlimited or has a definite limit, according as the surplus does or does not rapidly decrease. There is almost unceasing growth in organisms that expend relatively little energy and definitely limited growth in organisms that expend much energy. [There are many difficulties here, e.g., the apparent absence of a limit of growth in many very energetic fishes.]
(4) Among organisms which are large expenders of force, the size ultimately attained is, other things equal, determined by the initial size. [By initial size Spencer means the bulk of the organism when it begins to feed for itself.] A calf and a lamb commence their physiological transactions on widely different scales; their first increments of growth are similarly contrasted in their amounts; and the two diminishing series of such increments end at similarly-contrasted limits.
[But the further we penetrate into details, the more inevitable seems the conclusion that adult size is an adaptive phenomenon; in other words that growth has been punctuated by natural selection.]
(5) Where the likeness of other circumstances permits a comparison, the possible extent of growth depends on the degree of organization; an inference testified to by the larger forms among the various divisions and sub-divisions of organisms.
In connection with growth and its limit Spencer made a simple but shrewd observation, which seems also to have occurred to Prof. Leuckart and to Dr Alexander James. He pointed out, that in the growth of similarly shaped bodies the increase of volume continually tends to outrun the increase of surface. The volume of living matter must grow more than the surface through which it is kept alive, if the surface remain regular in contour. In spherical and all other regular units the volume increases as the cube of the radius, the surface only as the square of the radius. Thus a cell, for instance, as it grows, must get into physiological difficulties, for the nutritive necessities of the increasing volume are ever less adequately supplied by the less rapidly increasing absorbent surface. There is less and less opportunity for nutrition, respiration, and excretion. A nemesis of growth sets in, for waste gains upon, overtakes, balances, and threatens to exceed repair. Growth may cease at this limit, and a balance be struck; or the form of the unit may be altered and surface gained by flattening out, or very frequently by ramifying processes; or—and this the most frequent solution—the cell may divide, halving its volume, gaining new surface, and restoring the balance. In more general terms, growth expresses the preponderance of constructive processes or anabolism; increase of volume with less rapid increase of nutritive, respiratory, and excretory surface involves a relative predominance of katabolism; the limit of growth occurs when further increase of volume would prejudicially increase the ratio of katabolism to anabolism; at that point the cell restores the balance by dividing. And what is true of the unit applies also in a general way to organs, such as leaves which increase their surface by becoming much divided, and even to organisms which exhibit many adaptations for increasing their nutritive, respiratory, and excretory surfaces.
Development.—Growth is increase in bulk, development is increase in structure, and Spencer's chief induction in regard to development is that we see a change from an incoherent, indefinite homogeneity to a coherent, definite heterogeneity. "The originally like units called cells become unlike in various ways, and in ways more numerous and marked as the development goes on. The several tissues which these several classes of cells form by aggregation, grow little by little distinct from each other; and little by little put on those structural complexities that arise from differentiations among their component units. In the shoot, as in the limb, the external form, originally very simple, and having much in common with simple forms in general, gradually acquires an increasing complexity and an increasing unlikeness to other forms. Meanwhile, the remaining parts of the organism to which the shoot or limb belongs, having been severally assuming structures divergent from one another and from that of this particular shoot or limb, there has arisen a greater heterogeneity in the organism as a whole." Moreover, "whereas the germs of organisms are extremely similar, they gradually diverge widely in modes now regular and now irregular, until in place of a multitude of forms practically alike we finally have a multitude of forms most of which are extremely unlike." In other words, there is in individual development (ontogeny) some condensed recapitulation of the steps in racial evolution (phylogeny). Furthermore, in the progressing differentiation of each organism there is a progressing differentiation of it from its environment; it becomes freer from the environmental grip and more master of its fate. Here again there is an individual progress parallel to that seen in the course of historic evolution.
A general criticism must be made, that Spencer thought of the germ-cell much too simply. It is a microcosm full of intricacy; the nucleus is often exceedingly definite and coherent; the early cells are often from the first defined, with prospective values which do not change. The fertilised ovum has only apparent simplicity; it has a complex individualised organisation—often visible. No one can doubt that development is progressive differentiation, but it is rather a realisation of a complex inheritance of materialised potentialities than a change from an incoherent, indefinite homogeneity to a coherent, definite heterogeneity.
Structure and Function.—To the question, does Life produce Organisation, or does Organisation produce Life? Spencer answered that "structure and function must have advanced pari passu: some difference of function, primarily determined by some difference of relation to the environment, initiating a slight difference of structure, and this again leading to a more pronounced difference of function; and so on through continuous actions and reactions." As structure progresses from the homogeneous, indefinite, and incoherent, so does function, illustrating progressive division of labour. From an evolutionist point of view, Spencer argued that life necessarily comes before organisation; "organic matter in a state of homogeneous aggregation must precede organic matter in a stage of heterogeneous aggregation. But since the passing from a structureless state to a structured state is itself a vital process, it follows that vital activity must have existed while there was yet no structure: structure could not else arise. That function takes precedence of structure, seems also implied in the definition of Life. If Life is shown by inner actions so adjusted as to balance outer actions—if the implied energy is the substance of Life while the adjustment of the actions constitutes its form; then may we not say that the actions to be formed must come before that which forms them—that the continuous change which is the basis of function, must come before the structure which brings function into shape?"
But all such discussions of "structure" and "function" in the abstract tend to verbal quibbling. We cannot have activity without something to act, we cannot have metabolism without stuff. No one can tell what the first thing that lived on the earth was like, what organisation it had, or what it was able to do, but we may be sure that vital organisation and vital activity are only static and kinetic aspects of the same thing. It is quite probable, however, that there is no one thing that can be called protoplasm, for vital function may depend upon the inter-relations or inter-actions of several complex substances, none of which could by itself be called alive; which are, however, held together in that unity which makes an organism what it is. Just as the secret of a firm's success may depend upon a particularly fortunate association of partners, so it may be with vitality.[7]